1. Field of the Invention
The present invention relates to an implantable heart stimulating device wherein the stimulation rate is optimized dependent on sensed information.
2. Description of the Prior Art
High blood pressure, hypertension, is abnormally high blood pressure that puts stress on the tissue and organs in the body. Over time, high blood pressure can damage heart, lungs, brain, kidneys, eyes and blood vessels, as well as leading to heart disease, heart attack or stroke. High blood pressure usually does not cause symptoms and is often known as the “Silent Killer”. Organs and tissues can be damaged by high blood pressure without any felt symptoms until advanced stages of damage. Symptoms such as headache, blurry vision, abdominal and chest pain, shortness of breath, anxiety and dizziness may be experienced if the blood pressure reaches extreme levels. Many are symptoms usually not related to hypertension.
Blood pressure measurements are read as two numbers, the systolic and diastolic pressure. The higher number is called systolic pressure and the lower number is called diastolic pressure. Normal range of blood pressure is 120/80. High blood pressure is defined when the systolic pressure is greater than 140 and/or diastolic pressure is greater than 90.
In addition to thickening arteries, high blood pressure can cause hypertrophy of the heart. Hypertrophy is the enlargement of the heart because the heart is working too hard. This increases the risk for heart failure and arrhythmias. High blood pressure directly increases the risk of coronary heart disease (which leads to heart attack) and stroke, especially when it is present with other risk factors.
Although there is no single cause for high blood pressure, there are several risk factors that may affect blood pressure. There are two types of risk factors for high blood pressure: factors beyond control such as family history and age, and life style factors that can be controlled. The life style factors may include overweight, alcohol, smoking, diabetes and emotional stress.
The maintenance of blood pressure is highly complex and is dependent upon intrinsic, reflex, hormonal, renal and microvascular control systems. The complexity in the control of blood pressure is dependent upon the interaction from each of the control systems.
Development of hypertension is also suggested to depend on other mechanisms, including antidiuretic hormone (ADH) and baroreceptor resetting. The antidiuretic hormone is produced in the pituitary gland and regulates blood pressure through vasoconstriction and resorption of water. The pituitary gland communicates with the hypothalamus through neural connections, and thus the ADH release is under control of hypothalamic function. It is known that the hypothalamus is an important link between psychological events during emotional stress. However, a clear connection between emotional stress factors and hypothalamic control, either directly through the sympathetic nervous system, or indirectly with ADH release, has not been established.
Another mechanism leading to hypertension is that it is possible that the baroreceptor reflexes could be reset to maintain an elevated blood pressure for an indefinite time. There is suggested that there is no long term baroreceptive control and that resetting to a new level may occur. If baroreceptors are subjected to a maintained high pressure, their mean active rate returns to normal after a period of time. Evidences suggest that there may be a substantial resetting within as short time as 20 minutes.
In relation to the present invention the following US-patents may include valuable background information.
U.S. Pat. No. 6,275,733 discloses a dual sensor rate responsive pacemaker having an activity sensor, e.g. an acceleration-based sensor, and a metabolic sensor, such as a minute ventilation sensor. Determining the dual indicated rate is achieved by selecting between the two rates provided by these two sensors resulting in the use of the activity indicated rate during periods of low-level and brisk activity and the use of the metabolic indicated rate during periods of high exertion.
Another example of a dual sensor rate responsive pacemaker is disclosed in U.S. Pat. No. 6,055,454 relating to a cardiac pacemaker with automatic response optimization of a physiologic sensor based on a second sensor. The device has a first sensor for measuring a physiologic parameter reflecting metabolic demand and a second sensor for measuring a parameter reflecting the physical motion or activity of the patient, wherein the second sensor (activity sensor) is used to generate a dynamic target pacing rate which the first sensor is optimized to over time, thereby reducing the time constant for the adaptation of the first sensor and minimizing the amount of clinical time required to initialise the cardiac rhythm management device.
The normal physical response to the type of reactions mentioned above is an increase in blood pressure as well as an increase in heart rate. The same response may be observed when a person is preparing her- or himself for a significant physical activity.
In view of the above reasoning and in spite of all technical and physiological achievements in pacemaker technology of today, there is a need for a pacemaker responding to emotional reactions, emotional stress, such as nervousness, fear, joy, embarrassment and the like.